如何查看 dataframe 中是否存在列名，如果不存在则使用默认值创建列？

Question

I want to add a Column_4 when Column_4 does not exists in the dataframe. How do I search for it, and if no match create the new column?

Column_1   Column_2  Clolumn_3 

1             4         7
2             5         8
3             6         9 

Since Column_4 is not available, add Column_4 with value of 10

Column_1   Column_2  Clolumn_3  Column_4

1             4         7          10
2             5         8          10  
3             6         9          10

Answer 1

Check if the column name is in the columns list. If not make it 10:

if("Col_4" in df.columns):
    print("Col_4 exists")
else:
    df["Col_4"] = 10